1. Field of the Invention
This invention relates to packaging for heavy coils of strip material, and in particular to a packaging system that includes a skid supporting a heavy coil of strip material and stretch wrap plastic roped around the base of the coil and the corners of the skid. The package includes means for increasing the friction between the coil and the skid and preferably includes means for reducing damage to the stretch wrap material and the coil during transport.
2. Description of the Prior Art
Heavy cylindrical coils of strip material, such as aluminum, steel, paper and the like, are typically shipped by truck, rail and/or ship from the manufacturer of the coils to their users. Many of such coils may each weigh several thousand pounds. For example, a coil of aluminum strip material may weigh 30,000 pounds. The coils are usually covered with an outer packaging material such as plastic or paper to protect them from dirt and moisture.
To provide for transport by fork truck, truck, rail and overseas ship, the coils are rotated 90 degrees, resulting in the coil orientation being center axis vertical, and set on a pallet or skid. Typically, the skid is attached to the coil/load by means of vertical strapping (i.e., steel bands, plastic bands, web type bands) to keep the skid underneath its load during movements (i.e., shifts, impacts, vibration). The strapping nominally wraps underneath the center skid runner, up the front side of the load, across the top of the load (front-to-back), and down the back side of the load. A second strap wraps underneath and through the front-to-back center of the skid from right to left, up the left side of the load, across the top of the load (left-to-right), crossing the first strap, and down the right side of the load. Even with significant tension in the strapping material there is movement at the interface between the load and the skid. Movement at this interface, where there is load bottom packaging material between the load and the skid, abrades or wears on the load bottom packaging material.
Today's packages have countered abrasion on the bottom of the coil through increased layers of load bottom packaging material to minimize wear through over long distance transits. Also, the abrasion has been countered through various layers of padded material between the load bottom packaging material and the skid top. This is used in conjunction with the strapping tension to provide a means of grabbing the leading load edges and the skid deck board edges to keep the skid with its load. With enough load bottom packaging material and with enough pad thickness for typical hard impacts and/or long distance transit vibrations, these packages minimize packaging wear through and minimize the load-to-skid movements, making successful and reliable packaging systems. In an effort to reduce ergonomic health and safety packaging materials application issues and to reduce packaging materials for recycling, waste stream and cost benefits, a technology of stretch wrap roping is sometimes employed. Stretch wrap roping is stretch film pre-stretched, its width necked down into a small diameter rope, and tightly applied around the skid and its load. Since this rope is applied in a circular motion around the load and skid in the same approximate plane as the top of the skid, there is little securement of the skid vertically to the load. During transit of the stretch wrapped load, vertical movement of the package by fork truck hauling, rail car impact and the like sometimes results in vertical separation of the skid from the coil. The skid under compression pushes away from its load when the package is above the transit load surface. During this time of separation, any horizontal force against the skid or load separately will cause load-to-skid movement. As the load begins to again come in contact with the skid, which may now have different horizontal speeds, there is rubbing of the load bottom packaging material to the skid pad or rubbing of the load bottom packaging material against the load. Both of these are causes of packaging material abrasions. Also, during horizontal transit, impacts occur when the transit equipment suddenly slows or stops and the load is allowed to partially move in relation to the transit equipment. There is likewise load-to-skid movement and abrasion damage if the friction at the interface between the skid and transit load surface is greater than the friction at the interface between the load and skid. To successfully employ the stretch wrap roping packaging method, load-to-skid movements that result in load bottom packaging material abrasion wear through must be eliminated or significantly minimized.
Several different external events can damage the ropes in a stretch wrapped package. For example, non-level lifting of the skid load by a fork truck where the forks are tilted forward can damage the ropes when the skid load is initially lifted by the backs of the forks raising the first skid deck board away from its skid runners. This happens because the heavy load holds the rest of the skid flat against the floor surface. This uneven lift can lift the first deck board away from its runners as much as two inches before the rest of the load weight is captured by the front end of the forks. It can also break or bend the first deck board one to two inches back across its full left-to-right width. Stretch wrap roping wrapped around the corners of the first and last skid deck boards would become loose, pop over the deck board corners or be cut by severe deck board breakage, reducing or eliminating any rope tension needed for the package requirements.
Damage also occurs to stretch wrap roping when they are subjected to knife like actions from the normal sharp 90 degrees skid corners during transport movements. This can cut some or all of the ropes wrapped around a skid corner, reducing or eliminating any rope tension needed for the package requirements.
Damage to stretch wrap roping also occurs due to compressing and cutting of the ropes. The ropes are wrapped around the corners of skids and pass over the front and back faces of the skid runner and the front and back edges of the skid deck board. When skid loads are warehoused, stored or transported, two skids can be butted against one another, compressing or crushing the ropes passing across the front/back skid end faces. This can cut some or all of the ropes wrapped across the skid end faces, reducing or eliminating any rope tension needed for the package requirements.
The forks on fork lift trucks can also damage the stretch wrap roping. The ropes are typically wrapped around the corners of the skid runners and pass over the front and back edges of the skid deck board. The ropes pass across a void between the two skid faces that begins at the inside edge of the skid runner front face, crosses the void, and ends at the bottom edge of the skid deck board front face. This void, below the skid deck boards and inside the outside skid runners, is where the forks of fork trucks enter to lift the skid load. As these forks move in or out at the corner, where the ropes cross the void, the ropes rub across the top outside corners of the forks. This can cut some or all of the ropes in a skid corner void, reducing or eliminating any rope tension needed for the package requirement.
Accordingly, there is a need for an improved stretch wrapped coil/load package that reduces the vulnerability of such package to damage during transit and/or storage of the package.